As stored program-controlled switching systems have evolved, a wide variety of useful features have been developed to extend the communication capabilities such systems provide. Incoming calling line identification, a feature that displays the caller's number for incoming calls to a called customer station, allows selective acceptance of certain calls based on the calling number while other calls are either not answered or are routed to a message center. The feature is implemented by transmitting the calling line identification to the called customer station in a data message--for example, to an analog station during a silent interval between ringing or to an integrated services digital network (ISDN) station in the out-of-band D-channel used for call control signaling. Since customers typically remember only a few, frequently called telephone numbers, a related feature that provides a display of the caller name is substantially more useful to customers in deciding whether to accept a call. With a known call waiting feature where a caller-identifying data message is transmitted out-of-band, as for an ISDN station, a customer already engaged in an ongoing telephone conversation is informed of the caller identity for a second call that is coming in. Although such features provide customers with much greater control over their telephone communications, conventional analog stations, which represent a large majority of the customer stations in use today, are not equipped to either process or display data messages. In addition, modification of the normal human response of answering a ringing telephone, such that a customer glances at a display to determine caller identity before answering, is difficult, particularly for customers that use the features only infrequently.
In view of the foregoing, recognized problems in the art include the substantial communication station cost and the difficult human factors associated with the implementation of caller-identification features using data messages and requiring an advanced station display.